TIP122 is a medium-power linear switching device commonly used in low-speed switching circuits. It is a Darlington that can be used as a switch or amplifier, consisting of a cascade of two transistors in which the emitter of one transistor (PnP type) is connected to the base of the other transistor (NpN type), forming a Darlington Structure.

TIP122 is often used as a switch or amplifier. It belongs to a family of multifunctional transistors with high current and power handling capabilities. This device is widely used in a variety of circuits, including power supplies, drive motors, switching power supplies, and linear amplifiers.

TIP122 transistor has many good characteristics such as 5A collector current, maximum emitter-base voltage of 5V, maximum collector dissipation of 65 watts, minimum and maximum current gain equal to 1000. This transistor is designed for switching and amplification purposes.

Ⅰ.Specifications of TIP122

•Number of pins:3
•Configuration:Single
•Length:10.4 mm
•Height:9.15 mm
•Width:4.6 mm
•Package:TO-220-3
•Product Category:Darlington Transistor
•Transistor polarity:NPN
•Installation style:Through Hole
•Package/Box:TO-220-3
•Minimum operating temperature:-65℃
•Maximum operating temperature:+150℃
•Maximum DC collector current:5 A
•Maximum collector cut-off current:200 uA
•Dissipated power (Max):2000 mW
•Emitter-base voltage VEBO:5 V
•Collector-base voltage VCBO:100 V
•Collector-emitter maximum voltage VCEO:100 V
•Minimum current amplification (hFE):1000 @3A, 3V
•DC collector/Base Gain hfe Min:1000

Ⅱ.Features of TIP122

•Built-in protection diode: TIP122 has an internal protection diode that prevents reverse voltage peaks in the load, thereby protecting the circuit from damage.

•High reliability: TIP122 adopts PNP structure, which has good reliability and stability and is suitable for application scenarios with long-term stable operation.

•Low saturation voltage drop: In the on-state, TIP122 has a low saturation voltage drop, which helps reduce power consumption and improve efficiency.

•Voltage withstand capability: TIP122 generally has a higher voltage withstand capability and can operate at higher voltages, making it suitable for high voltage applications.

•Wide application: TIP122 is widely used as a switch or amplifier. Common applications include power supply, motor control, switching circuits and various power amplifiers.

•High current capability: It is capable of withstanding higher currents, usually in the range of several amps to tens of amps, making it suitable for circuits that need to handle large current loads.

•Strong power handling capability: TIP122 is a power transistor with high power handling capability and is suitable for circuit applications that need to handle larger power.

•TO-220 package: TIP122 is often packaged in TO-220. This package structure has good heat dissipation performance and easy installation, making it suitable for various circuit designs.

•High collector-emitter saturation voltage drop: The saturation voltage drop of TIP122 is generally around 1.5V, which means that in switching applications, it can effectively control large currents. In addition, the low value of saturation voltage drop also reduces power losses.

•Switching function: TIP122 is a power transistor that is often used as a switch to control the switching of high-power loads such as motors, lights, and heating elements. By applying a small current signal to its base, the current flow between its collector and emitter can be controlled.

Ⅲ.Working principle of TIP122

•The working principle of TIP122 is based on its internal structure and circuit design. TIP122 is an NPN Darlington transistor, which is composed of two transistors connected in cascade. Its working principle can be divided into three main areas: non-saturated area, saturated area and shutdown area.

•In the unsaturated region, when no voltage is applied to the base (B) or the applied voltage is low, the current between the collector (C) and the emitter (E) of TIP122 is very small and is in a cut-off state. At this time, TIP122 is equivalent to a high-impedance switch, which has little impact on the circuit.

•When a positive voltage is applied to the base and the voltage is high enough, TIP122 enters the saturation region. In this region, current begins to flow between the collector and emitter and increases as the base voltage increases. At this time, TIP122 is equivalent to a low-resistance switch that can be used to control large currents. Due to the Darlington structure of TIP122, it has a high current amplification capability, so that a larger load current can be controlled by applying a smaller control current to the base.

•When a negative voltage is applied to the base, TIP122 enters the shutdown region. In this region, the current flow between collector and emitter is cut off and the TIP122 is completely turned off. At this point, its impact on the circuit is almost zero.

Ⅳ.Absolute maximum rating of TIP122

Ⅴ.Electrical characteristics of TIP122

Ⅵ.Pin configuration of TIP122

•Pin1(Base):Controls the biasing of the transistor, Used to turn ON or OFF the transistor
•Pin2(Collector):Current flows in through collector, normally connected to load
•Pin3(Emitter):Current Drains out through emitter, normally connected to ground

Ⅶ.Application fields of TIP122

1.Power supply: TIP122 can be used in various types of power supply circuits, including linear regulators, switching regulators and switch-mode power supplies. It can withstand larger currents and powers and is suitable for power applications with higher demands.

•Linear regulator: In a linear regulator, TIP122 can be used as a control switch for the regulator to open or close the power path according to the output voltage needs.

•Switching Regulator: A switching regulator is an efficient and commonly used power supply design. TIP122 can be used as a switching transistor in such a system to quickly switch the power on and off to maintain the stability of the output voltage.

•Switch Mode Power Supplies (SMPS): SMPS are widely used in modern electronic devices due to their ability to provide efficient and adjustable power. The TIP122 can also be used as a switch or driver in this power supply type to help manage the power conversion process.

2.Power switch: TIP122 can be used as a power switch to control the external power supply to other components. For example, it can be used to control electronic equipment or electronic high-current switches to ensure the safe and stable operation of the circuit.

•Equipment power switch: In many electronic devices, such as TVs, stereos, computers, etc., TIP122 can be used as the main power switch to control the power on and off by controlling the voltage of its base, thereby controlling the working status of the entire device.

•Relay drive: TIP122 can be used to drive electromagnetic relays and indirectly control the switching of large current circuits or high voltage circuits by controlling the on and off of the relay. This application is common where isolation of control signals and main power is required, such as in automotive and industrial control systems.

•Load switching: In some application scenarios, it is necessary to switch different loads according to different working modes or functional requirements. TIP122 can be used as a load switching switch to select the load to be connected according to the control signal to achieve multi-functional control.

3.Lighting control: TIP122 can be used to control the brightness of lights, such as in stage lighting, car headlights and home lighting applications. By adjusting the size of the current, precise control of the light brightness can be achieved.

•Stage lighting: In stage lighting systems, the brightness and color of lights need to be controlled quickly and accurately. TIP122 can be used in conjunction with other circuit components (such as PWM (Pulse Width Modulation) controller) to achieve brightness adjustment by quickly switching the light on and off.

•Home lighting: In home lighting systems, TIP122 can be used to build dimmable luminaires. By combining with a PWM controller, smooth brightness adjustment can be achieved. In addition, it can also be connected to a microprocessor or intelligent lighting system to achieve automated brightness control and scene settings.

•Car headlights: In car headlights, although TIP122 is not directly used to adjust the brightness, it can be used to control the headlight switch, such as switching between high beam and low beam. If the brightness needs to be adjusted, an additional electronic control unit is usually built into the headlight design.

4.Thermostat and electric heater control: TIP122 can be used in thermostat and electric heater control circuits to control the on and off of heating elements to achieve temperature control and constant temperature functions.

•Thermostat: Thermostat is used to monitor and control the temperature of the environment. When the temperature is lower than the set value, the thermostat will send a signal to TIP122 to turn it on, thus turning on the power of the heating element for heating. Once the temperature reaches or exceeds the set value, the thermostat will send a signal to turn off TIP122, disconnecting the power supply to the heating element, thereby stopping heating.

•Electric heater: In electric heater control, TIP122 is used to control the heating element of the electric heater. By detecting the temperature inside the electric heater and comparing it with the set temperature, the control system will decide whether to turn on or off the power supply of the heating element through TIP122 to achieve constant temperature.

5.Power amplifier: Due to its high power handling capability, TIP122 is often used as the output stage driver of audio power amplifier to amplify audio signals to drive speakers.

6.Motor control: TIP122 can be used as a motor driver to adjust the speed and direction of the motor by controlling the current. In the fields of industrial machinery, robots, automobiles, etc., motor control is a very critical link. The excellent performance of TIP122 makes it a commonly used power switching device in these fields.

•Industrial machinery: In industrial machinery, motors are widely used to drive various mechanical devices. TIP122 can be used to control these motors to ensure that the machinery works as intended.

•Robots: Robot movements are usually driven by motors. TIP122 can be used to precisely control robot movements, such as movement, grabbing, etc.

•Automotive: In automobiles, motors are used for multiple functions like cooling fans, wipers, seat adjustment, etc. TIP122 can be used for the control of these motors to ensure they operate as required for vehicle operation.

7.Audio amplification: TIP122 can be used as an audio amplifier to amplify audio signals to drive speakers and sound systems. Its high voltage and high current characteristics make it capable of this task and provide sufficient power output for audio equipment.

•Signal amplification: As a power transistor, TIP122 has the ability to handle high voltage and high current, and is very suitable for audio signal amplification. It takes a low-level signal from a preamplifier or audio processor and amplifies it to a level high enough to drive speakers.

•Matched impedance: The audio amplifier also needs to match the impedance of the speaker to ensure maximum power transfer. The TIP122 can be used with an appropriate impedance matching network for optimal audio performance.

•Power output: The main task of an audio amplifier is to provide sufficient power output to drive speakers. The high power processing capability of TIP122 enables it to meet this demand, ensuring that audio signals are fully amplified to produce clear, powerful sound.

8.Switching circuit: TIP122 can be used as a switching element in a switching circuit to control the switching operation of high-power loads. For example, used in relay driver, lighting control, solenoid valve control, etc.

Ⅷ.Protection function of TIP122

1.Thermal stability: TIP122 is usually designed to work stably within a certain temperature range. This means it can operate at a certain level of heat without overheating damage.

2.Voltage resistance characteristics (VCEO): TIP122 is designed to withstand a certain voltage range. This means that under normal operating conditions, it can operate at the specified voltage without damage.

3.Over-temperature protection: Some designs may include over-temperature protection to prevent the TIP122 from being damaged due to overheating. This can be accomplished by adding a temperature sensor or overheating protection circuit.

4.Current resistance characteristics (IC): It can withstand a certain amount of current without being damaged. This is a key factor in ensuring that the current flowing through it in the circuit does not exceed its rating.

5.Overcurrent protection: In some cases, TIP122 may have overcurrent protection characteristics, which means that if the current passing through it exceeds its rating, it will automatically cut off the current to protect itself from damage.

Frequently Asked Questions

1.What are the precautions for TIP122?
In order for the TIP122 Darlington transistor to obtain good performance, it must be kept below the maximum rating. This transistor should not be used when the circuit is operating above 100V and the load is higher than 5A. The base resistor must be used to provide the required current at the base terminal.

2.What additional protective measures should be considered when using TIP122 in a circuit?
Additional protective measures may include using fuses, overvoltage protection circuits, overcurrent protection circuits, etc.

3.What are the alternative models of TIP122?
Alternative models of TIP122 include: TIP122TU, TIP122G, TIP122F, etc.